This is probably how I would go about it.

Most people who come to the Middle Ages through an interest in fantasy have a sort of "medieval pastiche" idea that mashes together different eras and places. Let's go with a vaguely 13th-14th century ethos: pre-printing press, pre or in the very early stages of gunpowder, moderate urbanization in some areas, a growing interest in the world beyond 'home'.

Read a couple of books on daily life stuff. These are generally going to be more in the popular vein. Ian Mortimer has A Time Traveller's Guide to 14th Century England and Greenwood Press put out a Daily Life in Chaucer's England volume that might interest you here. One of the things that is important to me, as a reader and a historian, in trying to evoke a past is to get a sense of how people saw the world differently. My favorite book for this is probably Jacques LeGoff's Medieval Civilization. Depending on your comfort level, Caroline Walker Bynum, Christian Materiality, will show you how WEIRD the Middle Ages could be, while still making perfect sense to people at the time. (You can skip the weighty theological chapters if you want. This is a serious history book, though, I'll warn you.)

And finally, the thing that very, very few "medieval European"-derived fantasy works get right is the overwhelming role of the Church in people's lives in the later Middle Ages. Even to the extent that urban artisans' guilds have it written into their foundation charters that they must pay for the performance of a Passion play or a specific saints' play every year. To get a sense of this, I would recommend the first section of Eamon Duffy's The Stripping of the Altars.

And finally, Ruth Mazo Karras, Sexuality in the Middle Ages: Doing Unto Others is a fantastic "social history" intro that will help create better characters, especially a sense of gender and sex dynamics, while being quite readable (well-written and an interesting topic) and won't throw you off the deep end.

Most of these should be accessible from a solid public library or through interlibrary loan if your branch lacks them; they are relatively affordable through Amazon as well, especially if you find used copies. :)

What time period and region are you looking for? For 14th century Italy I recommend "the merchant of Prato" by Iris Origo. Because Francesco (di Marco de Prato) Datini's archives had been burried under rubble for centuries, over 150,000 of his letters and trade documents survived. He was one of the richest Italian merchants of his time, so he didn't lead an absolutely "normal" life. What makes it so interesting (to me) however is that in the letters to his wife you can really see the evolution of their relationship, which suffers immensely under the strain of his constant travelling. Just like it would today. This is a really nice look into the (albeit abnormal) life of a wealthy 14th century merchant.